ESL is a small display device, which may replace paper labels and provide information of product names and prices. An ESL system typically includes more than thousands to tens of thousands of ESLs and a gateway. This gateway may be connected to a back-end point of sale (POS) system, update the contents of the ESLs via infrared or low-power wireless RF, to synchronize with product information of a POS system database. The store usually updates an ESL system at several fixed times, such as begins to update all ESLs' contents before the business hour 8:00 in the morning. The used wireless transmission medium bandwidth of ESL is limited, may not allow multiple ESLs to be updated simultaneously. In order to reduce power consumption, the ESL system may not always turn on the wireless module. There are two types of methods for updating ESL(s) to solve these problems. One type is the central assigned schedule, and the other type is the on-demand wakeup.
The central assigned schedule is directly assigned by the gateway, and then notifies each ESL the update time point. The ESL only turns on the wireless transceiver module at the time point assigned by the gateway and communicates with this gateway to update. When the ESL system begins the update, the gateway broadcasts each ESL the time of update. As shown in the example of FIG. 1, it is assumed that an ESL system includes three ESLs A, B, C. When the update begins, such as indicated by an arrow 110, all ESLs (i.e., ESL A, ESL B, and ESL C) together turn on their respective wireless transceiver module to receive the update schedule message broadcasted by the gateway, and ESL A, ESL B, and ESL C update in accordance with the time point specified in this message. Usually, the gateway issues a preamble signal before a predetermined update time, all ESLs at a same time wake up together triggered by an internal clock, after listening to the preamble signal, wake up again at a predetermined time to receive addresses and information according to the time point specified in the afore mentioned message, and return confirmation signals.
The ESL updating method of the central assigned schedule has a variety of variations. As shown in the example of FIG. 2, a power saving method in the ESL system includes a host computer to determine when messages will not be transmitted to any ESL within a time period p beginning from a time point t (step 202). The host computer transmits a power saving message to the ESL (step 204), and the contents in the message contain the time point t and the time period p. After the ESL receives the message, it enters the power saving mode beginning from the time point t, until passing the time period p (step 206). In other words, in this method updating the time point is not decided by the ESL itself, while the host computer directly determines the time point of the communication between the ESL and a gateway.
The on-demand wakeup method requires a wireless transceiver module configured on each ESL to receive update information, and also requires a receiver module configured to delicately receive specific wireless trigger signal(s). This trigger signal receiving module usually is a low power or passive radio frequency (RF) receive element, and the gateway or the host computer does not directly inform each ESL of the update time point. As shown in the example of FIG. 3, when a host computer wants to update an ESL 300, it first issues a trigger signal 322. The trigger receiving unit 342 in the ESL 300 receives this trigger signal, decodes and determines the recipient is itself, then wakes up a radio data communication unit 344 of the ESL 300 and begins to communicate with the base station to receive update information. Another technique discloses that a server host computer transmits a time-sharing control signal. After the ESL receives the control signal, it decodes the control signal to set next wakeup time point.
Many ESL update techniques have been proposed. In general, in the aforementioned two types of ESL update technology, the update procedure or period of the central assigned schedule relies on the gateway or the host computer arranges and notifies each ESL for each ESL update. When the schedule message that the gateway transmits to the ESL is interfered by interferences to lead to a communication failure, some or all ESLs may not receive the schedule, and the gateway needs to perform re-schedule and re-notification. In the actual application environment such as the environment of the store, due to the store environment being complex and full of changes, such as interference by consumers carrying all kinds of electronic appliances or crowded environment may completely obscure the line of sight of the ESLs and the gateway, the ESL is unable to receive the update schedule message, or unable to complete the update at the specified update time, and both may cause update failure for the affected ESL. Although there are corresponding solutions for this problem, for example, the staff completes the update manually with a hand-held device, but this method may increase the burden of labor cost. While the on-demand wakeup method requires additionally the receiver module configured and dedicated to receive the specific wireless trigger signal for each ESL, it increases the hardware cost of each ESL.